After excluding this task from your ETL container, you must rebuild your execution plan to exclude the task in the execution plan :
You could see step 8, 9 and 10 in the Oracle documentation : http://docs.oracle.com/cd/E28271_01/fusionapps.1111/e14849/dacexecutionplans.htm#i1061742

Sorry, in a first time you need to reassemble Subject Area using your inactived task (http://docs.oracle.com/cd/E28271_01/fusionapps.1111/e14849/dacsubjectarea.htm#CHDCECDC)
And after you could rebuild your execution plan.